Re: [Outreachy kernel] [PATCH] staging: fbtft: Replace udelay with preferred usleep_range

[Julia Lawall <julia.lawall@inria.fr>]

On Sun, 29 Mar 2020, John Wyatt wrote:

> On Sun, 2020-03-29 at 11:28 +0200, Julia Lawall wrote:
> >
> > On Sun, 29 Mar 2020, John B. Wyatt IV wrote:
> >
> > > Fix style issue with usleep_range being reported as preferred over
> > > udelay.
> > >
> > > Issue reported by checkpatch.
> > >
> > > Please review.
> > >
> > > As written in Documentation/timers/timers-howto.rst udelay is the
> > > generally preferred API. hrtimers, as noted in the docs, may be too
> > > expensive for this short timer.
> > >
> > > Are the docs out of date, or, is this a checkpatch issue?
> > >
> > > Signed-off-by: John B. Wyatt IV <jbwyatt4@gmail.com>
> > > ---
> > >  drivers/staging/fbtft/fb_agm1264k-fl.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/fbtft/fb_agm1264k-fl.c
> > > b/drivers/staging/fbtft/fb_agm1264k-fl.c
> > > index eeeeec97ad27..019c8cce6bab 100644
> > > --- a/drivers/staging/fbtft/fb_agm1264k-fl.c
> > > +++ b/drivers/staging/fbtft/fb_agm1264k-fl.c
> > > @@ -85,7 +85,7 @@ static void reset(struct fbtft_par *par)
> > >  	dev_dbg(par->info->device, "%s()\n", __func__);
> > >
> > >  	gpiod_set_value(par->gpio.reset, 0);
> > > -	udelay(20);
> > > +	usleep_range(20, 20);
> >
> > usleep_range should have a range, eg usleep_range(50, 100);.  But it
> > is
> > hard to know a priori what the range should be.  So it is probably
> > better
> > to leave the code alone.
>
> Understood.
>
> With the question I wrote in the commit message:
>
> "As written in Documentation/timers/timers-howto.rst udelay is the
> generally preferred API. hrtimers, as noted in the docs, may be too
> expensive for this short timer.
>
> Are the docs out of date, or, is this a checkpatch issue?"
>
> Is usleep_range too expensive for this operation?
>
> Why does checkpatch favor usleep_range while the docs favor udelay?

I don't know the answer in detail, but it is quite possible that
checkpatch doesn't pay any attention to the delay argument.  Checkpatch is
a perl script that highlights things that may be of concern.  It is not a
precise static analsis tool.

As a matter of form, all of your Please review comments should have been
put below the ---.  Currently, if someone had wanted to apply the patch,
you would make them do extra work to remove this information.

julia

>
> >
> > julia
> >
> > >  	gpiod_set_value(par->gpio.reset, 1);
> > >  	mdelay(120);
> > >  }
> > > --
> > > 2.25.1
> > >
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> > > .
> > >
>
>